A bridge that carries more than 40,000 cars per day over the Fox River in Green Bay, Wisconsin, has been closed indefinitely after part of it sagged early Wednesday morning.

A 400-foot swath of the Leo Frigo Bridge dipped across the road. Incredulous motorists quickly reported the problem to authorities. Jason Ruether, a trucker, was the first to call 911.

"I was headed north on the bridge, and it looks like there is a part that is sagging," he told the dispatcher.

"A part that is sagging?" she asked.

"Yes. Like, you know how most bridges have a hump in the middle? There's a section of the bridge that is actually a dip. The whole thing across."

Authorities found that a pier that supports the 33-year-old bridge had settled two feet in the river below. Wisconsin Department of Transportation officials said later in the day they do not believe the bridge is in danger of collapsing, but that the bridge could be closed for several months and possibly a year for repairs.

The Frigo was last inspected in August 2012 and categorized as "structurally sound," according to the Milwaukee Journal Sentinel. Here's a look at some of the best-known bridges across the U.S. that are in danger of problems, according to the AP report:

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